1. Field of the Invention
The present invention relates to a lighting unit and a projection display apparatus, which are provided with a plurality of solid state light sources that emits same color component lights.
2. Description of the Related Art
Conventionally, a technology using a plurality of solid state light sources (for example, laser light sources) has been known for display apparatuses such as a projection display apparatus. In addition, a technology for controlling solid state light sources in accordance with the luminance of an image (hereinafter, referred to as an image adaptive type light source control) also has been known.
In the image adaptive type light source control, when the luminance of an image is low, the light amount emitted from the plurality of solid state light sources is lowered. Generally speaking, in order to lower the light amount, the electric power supplied to the plurality of solid state light sources is reduced in an ascending order of the light emission efficiency of the solid state light sources. Accordingly, the power consumption of the display apparatus can be controlled.
Incidentally, it is known that, when using the solid state light sources such as LDs (laser diodes) that emits light having equal phases, the lights emitted from the solid state light sources cause a speckle on the irradiated surface of a screen or the like. In order to moderate such speckle, a technology of adjusting the distance of the solid state light sources and the irradiated surface has been proposed (for example, Japanese Unexamined Patent Application Publication No. Hei 7-115047). generally used in the conventional technique, the electric power supplied to the solid state light source having an unfavorable light emission efficiency is reduced. In other words, there may be a case where some of the solid state light sources are turned off.
Meanwhile, lights emitted from the plurality of solid state light sources generate speckles at respectively different positions. Thus, by superposing the lights emitted from the plurality of solid state light sources on each other, the speckles caused by these lights are moderated.
However, when some of the solid state light sources are turned off because of the unfavorable light emission efficiency, among the plurality of the solid state light sources, the effect of moderating the speckle by the superposition of light beams is decreased.